21639668 has 12 divisors (see below), whose sum is σ = 38082240. Its totient is φ = 10759032.

The previous prime is 21639647. The next prime is 21639679. The reversal of 21639668 is 86693612.

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 14396 + ... + 15827.

It is an arithmetic number, because the mean of its divisors is an integer number (3173520).

Almost surely, 2^21639668 is an apocalyptic number.

It is an amenable number.

21639668 is a deficient number, since it is larger than the sum of its proper divisors (16442572).

21639668 is a wasteful number, since it uses less digits than its factorization.

21639668 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 30406 (or 30404 counting only the distinct ones).

The product of its digits is 93312, while the sum is 41.

The square root of 21639668 is about 4651.8456552212. The cubic root of 21639668 is about 278.6657095984.

The spelling of 21639668 in words is "twenty-one million, six hundred thirty-nine thousand, six hundred sixty-eight".